From owner-svn-src-head@freebsd.org Mon Aug 15 20:09:10 2016 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 87C5BBBBA93; Mon, 15 Aug 2016 20:09:10 +0000 (UTC) (envelope-from badger@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 3E3611641; Mon, 15 Aug 2016 20:09:10 +0000 (UTC) (envelope-from badger@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id u7FK99lj014847; Mon, 15 Aug 2016 20:09:09 GMT (envelope-from badger@FreeBSD.org) Received: (from badger@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id u7FK99Yj014846; Mon, 15 Aug 2016 20:09:09 GMT (envelope-from badger@FreeBSD.org) Message-Id: <201608152009.u7FK99Yj014846@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: badger set sender to badger@FreeBSD.org using -f From: Eric Badger Date: Mon, 15 Aug 2016 20:09:09 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r304184 - head/sys/kern X-SVN-Group: head MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 15 Aug 2016 20:09:10 -0000 Author: badger Date: Mon Aug 15 20:09:09 2016 New Revision: 304184 URL: https://svnweb.freebsd.org/changeset/base/304184 Log: sem_post(): wake up the sleeper only after adjusting has_waiters If the caller of sem_post() wakes up a thread sleeping via sem_wait() before it clears the has_waiters flag, the caller of sem_wait() has no way of knowing when it is safe to destroy the semaphore and reuse the memory. This is because the caller of sem_post() may be interrupted between the wake step and the clearing of has_waiters. It will then write into the has_waiters flag in userspace after being preempted for some unknown amount of time. Reviewed by: jhb, kib, vangyzen Approved by: kib (mentor), vangyzen (mentor) MFC after: 2 weeks Sponsored by: Dell Inc. Differential Revision: https://reviews.freebsd.org/D7505 Modified: head/sys/kern/kern_umtx.c Modified: head/sys/kern/kern_umtx.c ============================================================================== --- head/sys/kern/kern_umtx.c Mon Aug 15 19:47:04 2016 (r304183) +++ head/sys/kern/kern_umtx.c Mon Aug 15 20:09:09 2016 (r304184) @@ -3123,7 +3123,6 @@ do_sem_wake(struct thread *td, struct _u umtxq_busy(&key); cnt = umtxq_count(&key); if (cnt > 0) { - umtxq_signal(&key, 1); /* * Check if count is greater than 0, this means the memory is * still being referenced by user code, so we can safely @@ -3136,6 +3135,7 @@ do_sem_wake(struct thread *td, struct _u if (error == -1) error = EFAULT; } + umtxq_signal(&key, 1); } umtxq_unbusy(&key); umtxq_unlock(&key); @@ -3235,8 +3235,6 @@ do_sem2_wake(struct thread *td, struct _ umtxq_busy(&key); cnt = umtxq_count(&key); if (cnt > 0) { - umtxq_signal(&key, 1); - /* * If this was the last sleeping thread, clear the waiters * flag in _count. @@ -3251,6 +3249,8 @@ do_sem2_wake(struct thread *td, struct _ error = EFAULT; umtxq_lock(&key); } + + umtxq_signal(&key, 1); } umtxq_unbusy(&key); umtxq_unlock(&key);